Hydrogen production by dissociation of steam with liquid tin

ABSTRACT

A process is described for the dissociation of steam by liquid tin to form hydrogen gas and solid tin dioxide. The wet hydrogen gas is collected and dried and the tin dioxide is subjected to reduction to form liquid tin that is then recycled.

United States Patent 1191 Spacil June 28, 1974 HYDROGEN PRODUCTION BY1,113,123 10/1914 lnnes 423/621 x I O E L] UH) 1,362,237 12/1920 Ros423/618 [AE F ST WITH Q 1,586,328 5/1926 Poppenhusen 423/621 2,072,3753/ l 937 [75] Inventor: Henry S. Spacil, Schenectady, NY. 2,565,9318/1951 1 2,984,544 5 1961 [73] Assignee: General Electric Company,3,017,250 1/1962 Schenectady, NY. 22 Filed; Jam 13 1972 PrimaryExaminer-Edward Stern 1 Attorney, Agent, or Firm-Leo l. MaLossi; JosephT, [21] PP No? 2171514 Cohen; Jerome C. Squillaro 52 us. c1. 423/657,423/618 1' ABSTRACT [51 Int. 'Cl COlb l/08 A process is described forthe dissociation of steam by [58] Field of Search 423/657, 618, 621, 565liquid tin to form hydrogen gas and solid tin dioxide. The wet hydrogengas is collected and dried and the [56] References Cited tin dioxide issubjected to reduction to form liquid tin UNITED STATES PATENTS that 18then recycled. 1,019,004 2/1912 Foerste rling 423/618 5 Claims, 1Drawing Figure HZ/HZO 7a COAFIDEwER L/qu/o rm] 1 T Pawns/esp cont. 6 l+6 p0,: 23 I 2 2 T Z2 PROM/ct? 1 f \11 11 u a; 2/ 1.14010 rm 2 0 e w IASH PATENTED JUN 2 8 1974 70 CONDENSER L 010 ml J STEAM POWDERED COALPRODU CE R BACKGROUND OF THE INVENTION The synthesis of hydrogen by theelectrolysis of water has in general been found to be uneconomic.Several alternative processes have been investigated; namely, (l) steamreforming of coal or hydrocarbons with the addition of oxygen followedby carbon dioxide scrubbing, (2) steam reforming of coal or hydrocarbonsin the presence of a carbon dioxide getter and (3) the dis sociation ofsteam by solid iron to form hydrogen and magnetite, the magnetite thenbeing reduced back to solid iron with producer gas formed by the partialcombustion of coal or hydrocarbons. The latter process has been the mostsuccessful, but involves the use of packed beds of granular material(iron or magnetite) to achieve a high gas/solid contact area. Sinteringof the granular solids in such packed beds constitutes a severeoperating problem.

Large volumes of low-cost hydrogen are increasingly required for suchapplications as the synthesis of high BTU content pipeline gas(essentially methane) by hydrogenation of carbonaceous material derivedfrom coal, and the hydrogenation of hydrocarbons during petroleumrefining. The cost of such hydrogenated products depends strongly on thecost of the relatively pure hydrogen required for the synthesis thereof.

SUMMARY OF THE INVENTION DESCRIPTION OF THE PREFERRED EMBODIMENT Thephysical and thermodynamic properties of tin and its oxides make ituniquely suited to use in hydrogen production through the dissociationof steam. An excess of steam is brought into contact with finelyatomized liquid tin, which had previously been reduced from solid tindioxide. The very high surface to volume ratio contact thus affordedavoids the problems of employing a packed bed reactor as in thesteam-iron pro cess.

The dissociation step is conducted by introducing finely atomized liquidtin (melting point -232C) and steam into contact with each other inreactor 10 which may be pressurized. The overall (unbalanced) reactionis as follows:

i-i ot e s p [H ,H20] (s) snow Excess steam is provided to drive thereaction to the right. The stability of solid SD02 relative to solid8110 at temperatures below 1.200C makes tin a very effective oxygengetter. I

SnO; collects in the hopper 11 for release via valve 12 as soon as theprocess is ready for continuous operation. Although heat may have to beapplied initially to reactor 10, this reaction is exothermic. The Ii /HO gas mixture is removed via pipe 13 and directed to a condenser (notshown) to remove the H content.

2 Although the gas mixture over the Sn(l) and SnO (s) consists primarilyof H and H 0, gaseous SnO will also be a minor constituent. Thispossible avenue for loss of tin through volatization can be neglected atdissociation temperatures below 700C. If higher temperatures are to beemployed, condensation and collection of the SnO are recommended.Operation at pressures in excess of 1 atmosphere does not afi'ectthepercent hydrogen in the gas over the liquid tin and Sn0 in the reactor,but such higher pressures will proportionally reduce the content of tinin the gas, since the vapor pressure of SnO over a mixture of liquid tinand Sn0 is nearly independent of total pressure. Thus, a pressurizeddissociation step is advantageous both to produce hydrogen'at elevatedpressures and to reduce tin losses.

The [H ,H O] gas mixture is removed from reactor 10 as the steam andliquid tin continue to be introduced at the desired rate. Oxidation ofthe liquid tin droplets by steam will result in formation of solid SnOparticles. Once ready for continuous operation, valve 12 is adjusted tocontinuously dispense this Sn0 from the dissociation reactor 10 toreduction reactor 16 wherein the solid tin dioxide is reduced to liquidtin preferably at atmospheric pressure as described hereinbelow.

In the embodiment shown a gaseous reductant is prepared in gasifier 17by the partial combustion with preheated air of a hydrocarbon or a coalproduct. The resultant reducing atmosphere is essentially producer gasconsisting primarily of nitrogen (N carbon monoxide (CO) and hydrogen (HAs shown air is introduced into the system via pump 18 and is movedthrough heater 19 to gasifier 17. The hot producer gas produced ingasifier 17 is conducted to hustle pipe 21 of reactor 16 via line 22.The tin dioxide powder is intro duced via pipe 23 and is distributed byperforated baf fies 24 to maximize contact with the reducing gassupplied via openings 26 leading from bustle pipe 21. The reducing gasis provided in excess to favor the production of liquid tin. If desired,all or part of the openings 26 may be located below the surface of themolten tin. In the former case, provision will have to be made toprevent entry of the liquid tin into these openings. In the latter case,means would have to be provided to prevent the entryof liquid tin intoopenings below the liquid level and to insure a baclopressure at holesabove the liquid level. t

The liquid tin resulting from the reduction of the Sn0 collects at thebottom of reactor 16 and is recir culated to reactor 11 via valve 27 andpump 28. A low BTU gas containing CO CO, H2,H20,fll'ld N is removed fromreactor 16 and may be burned to provide heat for reactor 16 or heater 19using means not shown. SnO powder traversing the open volume of reactor16 without being reduced should float on the liquid tin and remain incontact with the reducing atmosphere thereby insuring reduction.

Preferably, the temperature and pressure for the dissociation reaction(reactor 11) will be about 450 750C and 1 25 atmospheres, respectively.Operation at the elevated pressures provides the generated Hg already atpressure. The temperature and pressure in reactor 16 will be 700-1,100(.". and l-2 atmospheres, respectively. Production of the reducinggas would preferably be at similar pressures.

Other arrangements may be provided for reducing the SnO Thus,electrochemical reduction in a halide Snow) +C( 511(1) 992 (5);

The materials must be mixed and heated. Volatization of SnO can lead toa significant tin content in the gas above about 700C. Condensation andcollection of SnO is, therefore, required for the reduction step. whenusing solid carbon as a reductant.

Finely powdered SnO was mixed with 50/200 mesh coconut charcoal inproportions to give a percent excess of carbon over the amount requiredfor an oxygen/carbon ratio of 1.6 in the gaseous products of reduction(corresponding to the theoretically calculated value of 40 percent CO).About 10 grams of the mixture was packed loosely in an alumina crucible,the top of which was sealed with a porous plug. The crucible was heatedin a muffie furnace in a stream of flowing nitrogen, the porous plugpreventing the nitrogen from flushing away the gases evolved during thereduction before completereaction of excess CO with the SnO but didallow the reacted gases to escape slowly as the reduction progressed.Heating for two and a half hours at 630C did not result in anymeasurable reduction. Heating for 2 hours at 830C resulted in nearlycomplete reduction. The major portion of the liquid tin resulting fromheating .at the higher temperature was present in the form of spheresabout 2 to 3 mm in diameter. Some of the smaller spheres showed a brightmetallic surface, indicating that complete reduction had occurred, atleast locally.

Coal, which would normally be employed in this process for theproduction of producer gas in reactor 17 is not pure carbon, but alsocontains of the order of 20 atomic percent hydrogen and up to severalatomic percent sulfur. The presence of hydrogen in the producer gassupplied to reactor 16 is not detrimental to the reduction, since H willreduce Sn0 about as well as CO. The presence of the sulfur as H 5,however, will lead to the formation of gaseous SnS, and possibly (ifsufficient sulfur is present) to the formation of solid or liquid SnSSnS melts at 882C). The formation of solid SnS is fortuitous, the tinfunctioning as a getter for the sulfur and minimizing the release ofsulfur to the enviroment. The use of reduction temperatures above about600C will require condensation and collection of the gaseous SnS (andperhaps SnO as well) to prevent excessive Sn loss. The solid SnS canthen be treated with hydrogen to recover the tin with formation of H 8that in turn can be processed to recover the sulfur.

When the coal admitted to reactor 17 contains significant quantities ofsulfur, it may be preferable to introduce moderate quantities of CaCOalong with the coal. The idealized overall reaction (unbalanced) is aslo C( s) CaCO;(s-) [CO,CO (g) CaO(s).

In this manner the CaO produced acts as a getter for the sulfur byforming CaS. thereby reducing possible loss of tin by the formation ofvolatile SnS during reduction of the tin dioxide. The CaS canberecovered from the ash or converted to CaSO4 by roasting.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A process for the production of hydrogen comprising the steps of:

a. contacting steam with fine droplets of liquid tin at temperatures inthe range of from 450 to 750C to produce a mixture of hydrogen and steamand tin oxide, the tin oxide formed being predominately SnO and thesteam being supplied in excess to favor the formation of SnO b.contacting the tin oxide with a carbonaceous material at temperatures inthe range of from 700 to l,l00C to reduce the tin oxide to liquid tin,

c. recycling the liquid tin so produced into contact with steam in step(a),

d. removing the mixture of hydrogen and steam and g e. recoveringhydrogen therefrom.

2. The process as recited in claim 1 whereina gaseous carbonaceousmaterial is used.

3. The process as recited in claim 2 wherein the gaseous carbonaceousmaterial is prepared by partial combustion of coal in the presence ofCaCO to provide CaO by reaction with carbon content thereof.

4. The process as recited in claim 1 wherein a solid carbonaceousmaterial is used.

5. The process as recited in claim 1 wherein the mixture of hydrogen andsteam is generated under pressure ranging to as high as 25 atmospheres.

2. The process as recited in claim 1 wherein a gaseous carbonaceousmaterial is used.
 3. The process as recited in claim 2 wherein thegaseous carbonaceous material is prepared by partial combustion of coalin the presence of CaCO3 to provide CaO by reaction with carbon contentthereof.
 4. The process as recited in claim 1 wherein a solidcarbonaceous material is used.
 5. The process as recited in claim 1wherein the mixture of hydrogen and steam is generated under pressureranging to as high as 25 atmospheres.